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The levels of the winds are called "momentum levels", the ones for the scalar fields (like temperature and humidity) are called "thermodynamic levels". The are alternating with the lowest model level being a thermodynamic level, the highest a momentum level. See also wiki about model levels.
For more information have a look at the following publication:
Girard, C., A. Plante et al., 2014: Staggered Vertical Discretization of the Canadian Environmental Multiscale (GEM) Model Using a Coordinate of the Log-Hydrostatic-Pressure Type. Monthly Weather Review, DOI: 10.1175/MWR-D-13-00255.1